This invention relates to a method of creating NC data for a complex curved surface and, more particularly, to a complex curved surface NC data creation method in which a cutting path pattern is specified for every curved surface constituting a complex curved surface, and cutting is performed by moving a tool along the cutting path conforming to the specified cutting path pattern.
There are cases where it is required to machine a complex curved surface composed of a combination of two or more three-dimensional curved surfaces. FIG. 7 shows a side view (FIG. 7(A)) and a plan view (FIG. 7(B)) of a complex curved surface composed of a combination of two three-dimensional curved surfaces (hereinafter refered to simply as "curved surfaces") 1 and 2. The curved surface 1 has a frusto-conical shape, the curved surface 2 has the shape of a semicircular cylinder. There is also a boundary line 3. To machine this complex curved surface, the conventional practice is to designate one cutting path pattern on the entire complex curved surface, obtain points discretely on the actual cutting path based on the cutting path pattern, create NC data in such a manner that a tool will traverse the points continuously, and machine the complex curved surface on the basis of these NC data.
For instance, in the example of FIG. 7, the cutting path pattern is a group of straight lines which grow incrementally larger every a.sup.o in radial fashion from a center P.sub.c (FIG. 7(B)). Each straight line is a line segment from a point P.sub.i (i=1, 2, . . .) of radius r to a cutting boundary point Q.sub.i. The NC ddata for machining this complex curved surface are generated as follows:
NC data for an approach to a point P1; PA0 NC data for cutting from point P.sub.1 to a point Q.sub.1 ; PA0 NC data for a pick-feed to a point P.sub.2 ; PA0 NC data for cutting from point P.sub.2 to a point Q.sub.2 ; PA0 NC data for a pick-feed to a point P.sub.3 ; PA0 ...................... PA0 NC data for cutting from point P.sub.i to point Q.sub.i ; PA0 ......................
When NC data are thus created upon designating only one cutting path pattern for the complex curved surface and the complex curved surface is machined in accordance with the NC data created, an unnatural striped pattern is produced on the surface of the generated complex curved surface and the curved surface cannot be finished off attractively. It should be noted that if the stripes formed on the curved surface 2 are all parallel in the direction of the cylinder or all parallel in the circumferential direction, the surface will be finished off attractively. However, this will not be the case because only one cutting pattern (a radial pattern in the example of FIG. 7) is designated, and as a result, the surface will not exhibit an attractive finish.